1. Field of the Invention
The invention relates broadly to mounting of stained serial tissue sections for microscope observation but more specifically to an apparatus and method for covering film mounted tissue sections with transparent tape preparatory to microscope observation and subsequent storage and impregnating such sections during covering.
2. Description of the Prior Art
Stained histologic sections on glass slides are normally covered with thin cover glass. A synthetic adhesive is used when covering to adhere the cover glass and to keep the section clear for microscopic observation. When mounting the section on the glass slide, the stained section is kept moist with xylene until the synthetic adhesive is placed on and the cover glass is applied.
In 1954 when Cronar polyester film became available from E. I. duPont Company to serve as a base for motion picture film, the value of the Cronar film was seen for histologic sections due to being thin, e.g., .005 inch, flexible, clear, inert to staining solutions and heat resistant. The serial film-section procedure was worked out and beginning in 1956 Krylon clear acrylic spray plastic was used as a cover for the stained sections on 5-foot film lengths. After drying of the plastic coat, sections were observed under the microscope. The spray plastic was not adaptable to long 100-foot strips of film-sections as a cover. A thick Krylon base-plastic was obtained and a technique was worked out for dipping the stained film-sections in the thick plastic with the film-sections mounted on a stainless steel photographic developing reel. An automatic water bath for volume section cutting and film mounting was also developed. Reels of film-sections containing 100-foot lengths of film were later used and the mentioned thick Krylon plastic was used as a cover for the sections. However, histology technicians found it difficult to maintain the proper thickness of plastic on a continuous basis. Solvents used with the plastic were found to be toxic which required special ventilation such as a hood for discharging the fumes. Most tissue sections fall within 3 to 12 microns thickness. Section thickness was critically limited, however, to not more than 10 microns in the process just described. If the sections were more than 10 microns in thickness, the plastic would not cover the sections and under the microscope proper clarity was not obtainable. Also, uneven sections did not lend themselves to being covered by this technique.
An improvement upon the mounting methods and devices of the prior art is revealed in U.S. Pat. No. 3,552,247. This patent discloses mounting tissue sections directly onto a film base by a method and apparatus which eliminates the heretofore usual interim manual lifting of the cut sections from the blade and the usual water bath and manual floating steps. A microtome trough filled with a liquid receives the cut tissue sections directly from the microtome knife. The sections are floated across the trough and into contact with film which is passed through the trough.
Reference may be made to three publications of interest, namely: A.M.A. Archives of Pathology, March 1960, Vol. 69, pp. 239-247, "Thirty-Five MM. Film as Mounting Base and Plastic Spray as Cover Glass for Histologic Sections", John Phillip Pickett, H. T., and Joachim R. Sommer, M.D., Durham, North Carolina; Archives of Pathology, April 1964, Vol. 77, pp. 429-433, "Improved Film Strip Technique for the Laboratory", J. P. Pickett, H. T. (ASCP), W. B. Greene, N. T. (ASCP) and Joachim R. Sommer, M.D., Durham, North Carolina; and American Review of Respiratory Disease, Vol. 102, 1970, "SERIAL SECTIONS OF LUNG -- The use of a 70-Millimeter Film-Strip Technique for Large Tissue Sections", James W. Wilson and John Phillip Pickett. Also, see U.S. Pat. No. 3,498,860 which may be of general interest and U.S. Reissue Pat. No. Re. 24,906 relating to an adhesive tape useful in the invention.
As further background to the invention, reference is made to the Vickers cytology screening apparatus which was developed in 1968 by Vickers Instruments of Croydon, England. Although the Vickers apparatus was apparently never successfully marketed, it is noted that one aspect of the apparatus deals with the adhesive tape covering of a line of previously unembedded cells which are singularly mounted on a plastic strip so as to form a continuous hairline on the strip. Although the singular cell line of the Vickers apparatus is mounted on a plastic strip prior to adhesive tape covering, the cells are not adhered to a polyester film as in tissue mounting and the cells to be covered have previously undergone neither paraffin embedding, serial microtome slicing, nor a staining process which additionally serves to remove the paraffin embedding material. Such process has not dealt with the matter of impregnating tissue sections with optically clear adhesive and covering with an optically clear tape using such adhesive.
Note is also taken of an apparatus previously marketed as the Cytotrack Trace Laying System by Tetronics Research and Development Company, Lechlade Road, Faringdon, Berkshire, England. As with the Vickers apparatus elsewhere described, the Tetronics apparatus is concerned with mounting of cells as distinct from tissue sections which is the subject of the present invention. In using the Tetronics apparatus, cells are placed in a container, mixed with fixatives and stains, and the cells are allowed to drop from the container onto a film in a thin, hairline width trace. After being mounted on the film, the cells are sealed with a transparent polymer in a manner somewhat akin to prior art spray covering techniques. While such an apparatus and method have apparently been used successfuly for fixing, staining, mounting, and covering cells, they are basically limited to those specific purposes because of the substantially different problems encountered with mounting, covering, and viewing the conventionally paraffin-embedded, larger, non-uniform tissue sections and with impregnating such sections.
The referred to prior art deals with both light and electron microscopy techniques and while the concept of mounting tissue sections serially on film and covering the film mounted sections with plastic are known and have been practiced, it can readily be seen and appreciated that an expanding medical industry requires substantial improvements in method and apparatus for covering film mounted serial tissue sections and impregnating for optical clarity.